In certain environments, aluminum articles are subjected to contaminants that cause corrosion or other undesired effects on the aluminum surface. Unprotected aluminum can become corroded by acids, salts and other reactive compounds to develop pits or holes on and through aluminum surfaces. Ultraviolet (UV) radiation can cause discoloring of aluminum surfaces. Aluminum articles, such as heat exchangers, are often coated to protect aluminum and aluminum alloy surfaces. Such coatings provide resistance to corrosion caused by environmental contaminants or ultraviolet (UV) radiation or increase mechanical strength. These coatings can be applied to aluminum surfaces in a number of ways. Coating methods include electroplating, dip coating, spray coating and electrostatic powder coating. Protective coatings include conversion coatings and paint coatings.
Powder coating provides a less expensive way to coat aluminum articles. Powder coatings do not require special baths or large quantities of chemicals other than the powder coatings themselves. Powder coatings do not require solvents which can adversely impact air and water quality or can permanently damage aluminum articles. Traditional powder coatings have drawbacks, however. Prior to the present invention, powder coating formulations were generally optimized for one function (i.e. strength/bonding or UV resistance), but not both. Additionally, the traditional application of powder coatings did not provide the amount of control and uniformity that other coating processes possessed. Uniform levels of powder coatings are difficult to apply. In some cases, bare metal was left exposed following powder coating. This bare metal did not possess any of the protective characteristics that the powder coating provided. On the other hand, in some locations, the powder coating was excessively thick, which was detrimental for surface characteristics such as thermal and hydraulic properties.